The present invention relates to a passive optical network system and a wavelength assignment method, and particularly to a passive optical network system and a wavelength assignment method in which plural subscriber connection devices share an optical transmission line and communication is carried out by wavelength division multiplexing.
A Passive Optical Network (PON) includes an Optical Line Termination (OLT) and plural Optical Network Units (ONU) or Optical Network Terminations (ONT) (hereinafter, these are also called optical network units). A signal, as an optical signal, from a terminal (PC etc.) connected to the ONU is optically multiplexed to an optical fiber to the OLT from the ONU through an optical fiber and an optical splitter and is sent to the OLT. After the OLT performs various signal processings, communication from a terminal of an ONU to a terminal of another ONU of the PON or communication with a terminal of a NW is carried out.
As the optical multiplexing system, there is a system such as Time Division Multiplexing (TDM), Wavelength Division Multiplexing (WDM) or Code Division Multiplexing (CDM). For example, G-PON defined in ITU-T recommendation G.984.3 is a system in which different wavelengths are used for upstream/downstream communication, and in the communication between an optical line termination (OLT) installed in a station and a network unit (ONU) installed at each user, the communication of signals is carried out by time division multiplexing (TDM) in which signal communication time is assigned to each ONU (see, for example, non-patent document 1).
On the other hand, in the WDM system, between an OLT and an ONU, plural waves with different wavelengths are multiplexed to both an upstream signal and a downstream signal, and each ONU receives and transmits a specific wavelength to carry out communication with the OLT. An individual wavelength is assigned to each ONU from the OLT and the communication is carried out, so that it can be expected that a communication band is remarkably improved. One of methods of realizing the WDM-PON is a method in which one wavelength is assigned to each of an upstream signal and a downstream signal of each ONU, that is, the number of wavelengths used in one PON is made twice the maximum number of connected ONUs.
Besides, an example of initial setting of a path on a B-PON system is disclosed (see, for example, patent document 1).
[Patent document 1] U.S. Pat. No. 6,097,736
[Non-patent document 1] ITU-T recommendation G.984.3